Every day, 3800 robotic floats bob up and down, tracking temperatures in the world’s oceans, which sop up an estimated 90% of the heat from global warming. In the course of a decade, the international Argo array has provided one of the steadiest signatures of the effects of greenhouse gas emissions. But the floats go no deeper than 2000 meters, warded off by the crushing pressures at greater depths. Now, thanks to a $4 million investment from Paul Allen, the Microsoft co-founder, the National Oceanic and Atmospheric Administration (NOAA) will be deploying 25 next-generation floats, dubbed Deep Argo, that can survive down to 6000 meters, enough to reach the ocean floor at all but deep trenches. If this purchase proves the system viable, scientists hope NOAA will help support a full deployment of 1200 floats, searching for an answer on how global warming is influencing the ocean’s deepest, coldest depths
Unlike the last generation of Argo robots—aluminum, cylinder-shaped floats—the new Deep Argo floats, designed by Scripps Institution of Oceanography and Teledyne-Webb Research, can withstand the crushing forces of the deep ocean. Steve Piotrowicz, Program Manager of the U.S. Argo program since 2000, has watched the float design evolve to a glass sphere over the past few years to deal with the challenges of deep-sea diving.
A sphere is able to withstand much greater pressure than a cylinder because the pressure is distributed uniformly along the surface of the device, and glass is not only light and buoyant, but it withstands compression better than steel and titanium.
Beyond the deep ocean, the floats are also able to operate in some of the most inhospitable environments on Earth, such as the frigid waters of the Southern Ocean. To keep from battering itself against the ice, the float can detect conditions that indicate the surface ocean may have frozen over, and it will keep cycling below the surface until the ice retreats.
The new design was put to the test this past June aboard the Research Vessel Tangaroa operated by the National Institute of Water and Atmospheric Research of New Zealand. Piotrowicz accompanied a team of oceanographers deploying two prototype Deep Argo floats into the ocean northeast of New Zealand. In this part of the ocean, the seafloor is very flat with few obstacles for the floats to navigate around or over, and there are no strong deep sea currents that could drive dramatic changes in temperature.
Before the floats are deployed, the scientists first launch a CTD unit—“CTD” is an acronym for Conductivity, Temperature, and Depth. Based on a design that oceanographers have been using for decades, the CTD unit has 24 bottles attached to a large metal rosette wheel. The bottles collect water samples, while sensors at the bottom of the unit measure temperature, depth, and salinity. A data cable connects the device to a computer on the ship.
Piotrowicz hopes that in years to come, Deep Argo will achieve global coverage, much like the present of generation of Argo floats. The fledgling U.S. Deep Argo program only has funding to deploy about 12 floats per year. To meet current science objectives, the global fleet will likely require on the order of a thousand floats
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